Re: [PATCH v2 04/18] xprtrdma: Prevent inline overflow

[Sagi Grimberg <sagi@grimberg.me>]

> When deciding whether to send a Call inline, rpcrdma_marshal_req
> doesn't take into account header bytes consumed by chunk lists.
> This results in Call messages on the wire that are sometimes larger
> than the inline threshold.

I'm not sure I understand why you need to account the chunk list size
when deciding on the inline data size., aren't chunk lists for remote
access only?

Is this a first-burst kind of functionality?

> Likewise, when a Write list or Reply chunk is in play, the server's
> reply has to emit an RDMA Send that includes a larger-than-minimal
> RPC-over-RDMA header.
>
> The actual size of a Call message cannot be estimated until after
> the chunk lists have been registered. Thus the size of each
> RPC-over-RDMA header can be estimated only after chunks are
> registered; but the decision to register chunks is based on the size
> of that header. Chicken, meet egg.

:)

> The best a client can do is estimate header size based on the
> largest header that might occur, and then ensure that inline content
> is always smaller than that.

Isn't that a big loss?